Field of the Invention
The present invention relates to an image forming apparatus with a power saving mode.
Description of the Related Art
Image forming apparatuses include a single function printer (SFP) and a multifunction printer (MFP). The SFP is specialized in a printer function to form an image by an electrophotography process. The MFP is configured by combining an image reading unit etc. with an SFP.
Control boards of the SFP and MFP include a controller board that controls the entire apparatus and an engine board that controls a printer unit only. A CPU is mounted on each of the controller board and engine board. Then, the printer unit is controlled by a command from the controller board when the two CPUs communicate. Since the SFP and MFP are different in a function, the controller board of the SFP and the controller board of the MFP are different in a configuration. On the other hand, since specifications of the printer units are common in the SFP and MFP, it is preferable that the engine board of the SFP is also used as the engine board of the MFP from a point of view of cost reduction.
Japanese Laid-Open Patent Publication (Kokai) No. 2006-172173 (JP 2006-172173A) discloses a conventional technique about an SFP or an MFP that performs serial communication between a master processor equipped with a CPU and a slave processor. The technique disclosed in this publication supplies a strobe signal on serial communication to an input terminal of a clock monitoring means. The strobe signal is a synchronizing signal indicating start of communication or a synchronizing signal actively controlled during communication. The clock monitoring means is a means for monitoring a toggle operation at a certain interval, and is represented by a watchdog timer. Since the conventional technique gives two functions to the strobe signal by sharing the strobe signal with a clock for the watchdog timer, the number of signal lines is reduced.
Incidentally, the sleep mode is installed on an SFP and MFP in recent years. When a standby state of an apparatus continues for a long time, the apparatus automatically shifts to the sleep mode in which electric power is supplied only to the minimum units that include a controller board and is not supplied to the other units. The timing at which the mode is shifted to the sleep mode (hereinafter referred to as a “power saving mode”) from the standby mode is set up by a user, for example.
When an SFP or an MFP performs a print job after turning power ON or releasing the power saving mode, a printer unit performs a multiple pre-rotating operation as a pre-process. The print job is performed after finishing the multiple pre-rotating operation as a preparation operation.
However, since the multiple pre-rotating operation drives the main driving units of the printer, operation sound is generated. Since a job of the SFP is limited to a print job, the multiple pre-rotating operation is certainly needed after releasing the sleep mode. However, jobs of the MFP include jobs without a print operation, such as a job that transmits an image read by an image read unit to a personal computer and a job for a facsimile transmission after releasing the sleep mode. Such a job does not need the multiple pre-rotating operation essentially. Accordingly, there is a problem that the operation sound of an unnecessary multiple pre-rotating operation becomes noise for a user in a case where the operation of the printer unit is not needed. Moreover, since an electric current is also supplied to a fixing device during the multiple pre-rotating operation, the multiple pre-rotating operation performed before a job without a print operation wastes energy.
In order to prevent an unnecessary multiple pre-rotating operation, it is preferable that the controller board transmits a control signal that controls the printer unit to perform or not to perform the multiple pre-rotating operation to the engine board after releasing the power saving mode. Such a control signal is called a WAKE signal. Then, when the WAKE signal transmitted after releasing the power saving mode is Low level, the printer unit does not perform the multiple pre-rotating operation. On the other hand, when it is High level, the printer unit performs the multiple pre-rotating operation. As a result of this, the engine board should check a logic of the WAKE signal when the power saving mode is released, and should select operation according to the logic.
However, implementation of the WAKE signal needs an output port for the controller board, needs an input port for the engine board, and needs to add a signal line to the interface that connects the controller board with the engine board.